A standard filter press has a plurality of compartments defined between filter plates and each subdivided by a filter cloth or screen into an input compartment and an output compartment. The filter plates have ridged and grooved front surfaces turned toward the filter cloth and forming drainage channels in the output compartment. The filtrate is introduced into the input compartment and the liquid phase is extracted along the channels from the output compartment, with the solid phase of the suspension left on the filter cloth.
In order to clean such a filter the center panels of the filter plates are constituted as membranes and the plates are sufficiently elastic or resilient that these center panels can be pushed toward each other to press the solid phase into a filter cake that can be back flushed or otherwise emptied from the machine. This forward deflection to compress the solid phase is effected by pneumatically or hydraulically pressurizing another compartment formed between the back face of the plate and a relatively rigid support plate located immediately behind each filter plate.
As described in German patent document 3,220,487 the filter plate comprises the relatively thin center panel and a relative thick peripheral frame connected to this panel by a web lying in the plane of the panel. This connecting web is subjected to considerable bending and tension when the back compartment is pressurized and the plate is deformed to pack the solid phase, in particular when the filter is only partly full. As a result it has a short service life so that the plate can be expected to wear out at this location. When there is a central input for the filtrate, it is possible for the filter to fill around this input and not work at all.